The present invention relates to flood resistant building structures, and more particularly to building structures that are floatable such that damage is reduced in the event of a flood.
The invention has been developed primarily for use with residential structures in relatively flood-prone areas, and will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to use in this field.
Historically waterways have been useful for transportation of goods and people, and as a water supply for industry and agriculture. Land near waterways, lakes and the like also tends to be aesthetically pleasing. For these and other reasons, early human settlements tended to be built relatively close to waterways, and rivers in particular. This pattern has been repeated over time, notwithstanding improvements in land-based transport and water distribution networks.
Unfortunately, land adjacent waterways and in low-lying areas is relatively prone to flooding. Flooding can cause tremendous emotional and financial damage as structures and businesses are damaged, and personal property destroyed. Worldwide, the annual cost of flood damage and displacement runs into many billions of dollars every year. For building occupants and owners this is a particularly pressing problem as it is frequently difficult or at least expensive to obtain insurance cover against flooding. Naturally, the more prone to flooding an area is, the more difficult it will be to obtain such insurance.
One of the difficulties of planning for buildings in flood prone areas is that floods occur at irregular intervals and that the magnitude of less common floods can be substantially greater than those floods that occur over a typical human lifetime.
Conventional buildings, such as the house 200 shown in FIG. 1, are built with a floor level 205 at or near ground level 125. Clearly this is an undesirable form of construction for use in flood-prone areas, simply because flood waters of any substantial depth can advance higher than the floor level. Further, such buildings can obstruct the flow and egress of flood waters, potentially exacerbating flooding problems. Regulatory bodies may therefore require an xe2x80x9cabove-gradexe2x80x9d construction.
An example of the usual approach to above-grade construction is shown in FIG. 2. A conventional building 100 includes a superstructure 105 constructed atop piers 115 that are fixed into foundations in the underlying ground. This arrangement is used to permanently maintain the building superstructure 105 and its associated floor structure 110 at a predetermined height above grade level 125. The piers 115 are often braced 120 to reduce lateral movement in, for example, high winds. This arrangement allows low level floodwater to pass beneath the building without actually flooding the superstructure 105 or floor structure 110. This arrangement has been used since early civilisation, without fundamental changes other than in building materials and construction methods.
However, there are a number of specific disadvantages with the arrangement of FIG. 2, such as:
(a) flood waters may advance higher than the raised floor level 110;
(b) the fixed piers 115 may be unsightly, especially if they are relatively high to deal with correspondingly high potential flood water situations;
(c) building regulations may place restrictions on maximum roof or floor heights, which can prevent sufficiently long piers being used;
(d) in very low-lying areas or areas prone to deep flooding the required pier height can be considerably higher than is desirable given the need for day-to-day access for residents.
In an effort to mitigate some of the problems with fixed elevated structures, various techniques have been proposed for constructing floatable buildings at grade level on dry land.
One such technique is disclosed in U.S. Pat. No. 5,347,949 by Paul K. Winston (hereinafter referred to as xe2x80x9cWinstonxe2x80x9d). As shown in FIG. 3, Winston discloses a prefabricated modular housing unit 300 for use in flood prone areas. In particular, there is shown a cross section of a floatable housing unit 300 floating on floodwater 305. The housing unit 300 uses flotation elements 310 formed from plastic liners 320 filled with foam 315. The flotation elements 310 are seated underneath a foundation 325 of wooden beams fastened to a conventional floor joist system.
The housing unit 300 is anchored to the building site through a series of telescopically extendible piers 330, in combination with a series of wooden pilings 340 that serve as a fixed dry-land foundation.
During a flood, the flotation elements 310 displace water until the entire weight of the building""s superstructure is supported by them. As the flood waters continue to rise, the housing unit 300 is raised by the flotation elements 310, which act as pontoons. The building is maintained in a substantially constant lateral position by the extendible piers, which slide telescopically from their submerged recesses as the housing unit 300 is raised by the flotation elements 310.
The Winston arrangement suffers from a number of disadvantages. For example, the extendable telescopic piers 330 are exposed even in the retracted position, and can be subject to ingress of moisture and dirt over time. Moreover, the exposed portions of the piers 330 can corrode, inhibiting their subsequent extension. Additional corrosion can occur as floodwater rises and the telescopic piers 330 extend. Water even fills the extended telescopic piers 330, apparently to provide a damping effect. However, this also washes away protective lubricants, further accelerating corrosion.
In addition the foam filed plastic liners are potentially prone to degradation over the long term. Under normal conditions, access for inspection and maintenance to these units is limited. The foam liners also provide a ready means of ingress for termites to the building structure in regions where termites are active.
In addition, the Winston housing unit 300 is unstable when it floats and requires careful balancing of loads. On the heavy portion of the housing unit 300, larger foam flotation elements 310 are required. The load distribution in the housing unit 300 shifts as the building is furnished. To compensate for shifting loads, air bladders 350 at each corner of the housing unit 300 are required. The air bladders 350 are filled with proper amounts of air to provide a stable and level flotation. This is complex, inefficient and time consuming as it requires a compressor, a level measuring device and fine tuning (i.e. repeated inflation and deflation) of each air bladder to achieve a level flotation. For example, inflating a first air bladder often requires re-adjusting the air in the remaining three air bladders 350, which in turn can necessitate further re-adjustment of the first air bladder.
Furthermore the Winston disclosure does not reveal a manner whereby the additional buoyancy forces applied to the floor structure 325 from the bladders 350 can be transmitted laterally to support movable loads, such as people and furniture that are not directly over the bladders 350. Thus, with the disclosed floor joist system, it is likely that there will be relative movement within, and hence physical distress to, the housing unit 300.
Furthermore, the potential for a low pressure region between the ground, pontoons and floor of the Winston arrangement suggests that in some circumstances the housing unit 300 may not float.
Another technique proposed for constructing floatable buildings at grade level on dry land is disclosed in U.S. Pat. Nos. 5,647,693 and 5,775,847, by Herman Carlinsky et al (hereinafter referred to as xe2x80x9cCarlinskyxe2x80x9d). As shown in FIG. 4, Carlinsky discloses a prefabricated building 400 including a watertight basement 405, the floor and walls 410 of which are of unitary concrete constriction. Rollers 415 are attached to outer surfaces of the watertight basement (405).
As floodwater rises or recedes, the rollers 415 roll along a guide post/ratchet system 420 located adjacent respective corners of the watertight basement 405. The guide system 420 maintains the building 400 at or near the height reached during a peak of a given flood.
One embodiment disclosed by Carlinsky includes pressurised cylinders 430 for lifting the building 400 prior to a surge of floodwater and for breaking any vacuum formed under the basement 405 as the building first lifts under the influence of floodwaters.
The Carlinksy system suffers a number of disadvantages. For example, to reposition the building at ground level after even a minor flood, it is necessary to deploy lifting mechanisms at several points around the building perimeter. The provision of cranes or other lifting devices to achieve this is both costly and inconvenient.
Furthermore, Carlinsky does not disclose the manner in which the buoyancy forces generated during a flood are transferred from the unitary basement structure 405 to the rest of the building 400. Carlinsky also fails to disclose the way in which loads from the building superstructure are transmitted through the basement 405 to the post/ratchet system 420 in the post flood situation. It is likely that excessively large concrete cross sections will be required to achieve a sufficiently stiff and strong basement structure 405 if the building 400 is constructed according to the disclosure.
In addition, all debris under collecting under the basement during a flood must be removed before the building can be lowered into its normal position after a flood event.
The method of construction using a monolithic concrete basement 405 is potentially expensive and inappropriate on some sites or in some regions.
In addition, the Carlinsky system is cumbersome and potentially unreliable. The system relies on the actuation of pressurised systems 430 and a series of rubber seals, all of which may not reliably activate in a flood that may occur many decades after the building is constructed.
Both the Winston and Carlinsky systems suffer from another serious disadvantage. In each case, where flood waters continue to rise once the structure has reached its uppermost limit of travel, the buoyancy forces continue to rise. According to buoyancy theory, these forces are proportional to the amount of water displaced, and can therefore reach relatively large values. Three possible scenarios are then possible. Firstly the building subject to high water may simply float away off the top of its guides. Alternatively, the building can be constrained at the upper limit of its travel, but then risks being violently and unpredictably torn from the constraints under the influence of increasing flotation forces. Both scenarios are potentially disastrous and are worse than the consequences of the flooding event that the systems were trying mitigate. A final option is to construct the building and its guidance system robustly enough to resist the maximum buoyancy forces. However, this is relatively expensive.
A technique is also proposed for constructing a building or other structure that is supported above the water level during a flood. This is disclosed in U.S. Pat. No. 6,050,207, by Vance H. Mays (hereinafter referred to as xe2x80x9cMaysxe2x80x9d). As shown in FIG. 5, Mays discloses a building or other superstructure 1801 supported upon a frame 1803 supported by a series of pontoons 1809. The pontoons slide within casings 1802 and float on a controllable volume of liquid contained within the casings. Columns 1808 slide through a series of bearings and seals incorporated in a cover attached to the top rim of the casing. The frame 1803, and hence the building superstructure 1801 is supported upon the columns and restrained in a lateral position by the columns via the bearings in the casing.
When the building is raised the columns transmit the weight of the superstructure via the pontoons to the liquid in the casing. At other times the columns transmit this weight directly to the casing and thence to the foundation.
As the amount of liquid is varied within the casings the pontoons rise or fall, thus causing the superstructure to rise or fall. The amount of liquid in the casing is altered via a series of valves and pumps, these being actuated by electrical batteries and/or generators 1807. Sensors 1804 monitor the relative level of the structure and other sensor 1805 monitor the flood water level. Manual or computer control 1806 activates the system and acts to keep the structure level.
The Mays system suffers a number of disadvantages. For its basic operation the system relies upon a relatively complex system of electrical systems, mechanical systems and structures. Furthermore the flotation units are normally installed under the ground and so under normal conditions access for inspection and maintenance to these units is limited. Hence, these may not reliably activate in a flood that may occur many decades after the structure is constructed. This could result in damage to the superstructure or to the flotation units themselves.
For example failure of any one of the bearings, seals, valves, monitoring or control systems could cause one of the pontoons to xe2x80x9cstickxe2x80x9d. Alternatively failure of a seal or valve could cause an uncontrolled volume of fluid to enter the casing causing one pontoon to rise excessively. In either case this could cause damage to the flood support systems or to the building structure itself.
In addition the systems and structures disclosed by Mays are likely to be expensive relative to the cost of the superstructure. This has the potential to render the system economically unfeasible in many situations.
The Winston, Carlinsky and Mays systems all suffer from a disadvantage in that they allow free vertical movement of the structure under the influence of buoyancy forces but they do not disclose a method whereby the building structure is prevented from upwards movement under the influence of wind loads. As a consequence potential exists for excessive damage to the building structure during a wind storm.
It is an object of the present invention to overcome or at least substantially ameliorate one or more of the disadvantages of the prior art.
According to a first aspect of the invention, there is provided a flood resistant structure for use in flood-prone areas, the structure including.
a plurality of guide posts extending substantially vertically from support foundations;
a building structure disposed adjacent the guide posts;
flotation means disposed under or within the building structure, the flotation means being of sufficient buoyancy to enable the building structure to float on water when necessary;
guide means linking the building structure and the guide posts; and
support means associated with the guide posts;
the flood resistant structure being configured such that, in a usual mode of operation, the building structure is supported by the support means and thereby the guide posts until flood waters rise to a level sufficient to cause the weight of the building structure to be transferred from the support means to the flotation means, wherein further increases in flood-water level cause the building structure to float upwardly whilst the guide means maintain the building structure in a relatively stable lateral position with respect to the guide posts.
Preferably, the guide posts are disposed adjacent one or more corners of the building structure.
In a preferred form, the support means take the form of corbels disposed on respective guide posts at a predetermined height, such that the building structure is supported at a predetermined height by the corbels during the usual mode operation of the flood resistant structure.
Preferably, the flotation means takes the form of air filled compartments formed in a floor area of the building structure.
In a particularly preferred embodiment, the flood resistant structure further includes retention means configured such that, once the building structure has floated beyond a predetermined height in relation to the guide posts, it is prevented by the retention means from lowering with the flood waters as they recede. Preferably, the retention means takes the form of a ratchet and pawl, or spring-loaded corbel mechanism.
In another preferred embodiment, the flood resistant structure further includes selective flooding means for allowing at least partial flooding of some or all of the flotation means.
Further aspects of the invention are disclosed in the accompanying detailed description and in the numbered paragraphs at the end of the specification.